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Plastering is a skill that requires both knowledge and practice. It involves applying different types of plaster to internal walls and ceilings to create a smooth, even surface ready for decorating. Here are some of the most common basic plastering techniques for plastering a wall used in the UK.
Two Coat Plastering (Wet Plastering)
This is one of the most traditional plastering methods, hence often referred to as ‘traditional plastering’. It involves two layers of sand and cement plaster, hence the name. The first coat, also called the ‘scratch coat’ or ‘base coat’, is applied to the wall or ceiling. Once it’s partially dry, it’s scratched with a comb to create a key for the second coat, or ‘finish coat’. The finish coat is then applied and smoothed off.
Preparation: Before starting the plastering process, it’s important to properly prepare the surface. This involves removing any existing paint or wallpaper, repairing any damage, and ensuring the surface is clean and dry. Depending on the type of wall, a primer or sealer may need to be applied first to help the plaster adhere properly.
First Coat – Scratch Coat: The first coat, also known as the scratch or base coat, is applied using a plasterer’s trowel. This coat is a mix of sand and cement, providing a robust and sturdy undercoat for the finish plaster to be applied on top. The mixture is usually 4 parts sand to 1 part cement, along with a plasticiser which makes the mixture more workable and adhesive. The thickness of the first coat is usually around 10-12mm. It’s important to ensure that the coat is applied evenly. After application, the plaster is left to dry slightly but not completely.
Once it’s started to set (but while it’s still soft), the plaster is then scratched using a tool often called a “devil float” or “scarifier”. This tool has small teeth that create grooves in the plaster. This process is what gives the coat its name, and it’s crucial because it creates a ‘key’ that helps the next coat adhere to the surface better.
Check out this list of plastering tools.
Second Coat – Finish Coat: The finish coat, which is the second coat in the two coat plastering process, is typically made of a finer sand and cement mix, often with the addition of lime to make it more workable and give it a smoother finish. This coat is typically 2mm to 3mm thick. The plasterer uses a clean, wet trowel to apply the plaster and smooth the surface.
This coat is also left to dry slightly before it is smoothed again using a plasterer’s float – a flat, handheld tool. This is often done with a bit of water to lubricate the surface and help achieve a smoother finish. This process, called ‘trowelling up’, may be done several times to achieve the desired smoothness.
After the final coat, the plaster needs to be left to dry completely, which can take several days depending on conditions such as the temperature and humidity levels.
Wet plastering is a skill that requires experience to get right, particularly when it comes to getting a smooth, even finish. The plaster also needs to be mixed to the right consistency – too wet and it won’t stick properly, too dry and it will be hard to work with and may crack as it dries. But when done correctly, it gives a very solid, durable finish that can last for decades with minimal maintenance.
Skimming is a thin coat of plaster applied over existing plaster to smooth out minor imperfections and create a surface that’s perfect for painting or wallpapering. Skimming is usually applied with a plastering trowel in two coats – the first is allowed to semi-dry before the second coat is applied.
Preparation: The preparation for skimming involves ensuring the surface to be skimmed is clean, free of dust, dirt, or any loose materials. This may involve washing the walls, scraping off loose plaster, filling any large holes or cracks, and possibly applying a coat of PVA (Polyvinyl Acetate) glue solution to help the plaster adhere to the surface better.
First Coat: The first coat, also called the base coat, is applied thinly using a plastering trowel. The plaster used for skimming is different from the sand and cement mixture used for wet plastering. It’s typically a gypsum-based plaster, sometimes referred to as ‘finish’ or ‘skim’ plaster. This plaster is smoother and easier to work with, allowing for a finer finish.
The plaster is applied at an angle, with the trowel being held at about 10-30 degrees to the surface. The plasterer applies pressure to the trowel to spread the plaster evenly across the surface, filling in any imperfections. The first coat is usually around 2mm thick. Once applied, the plaster should be left to dry slightly, until it’s firm but not fully set.
Second Coat: The second coat is applied in much the same way as the first. It’s also around 2mm thick, giving a total thickness of about 4mm for the two coats. The second coat is applied before the first coat fully dries – this helps the two layers bond together better.
Once the second coat has been applied and is slightly dry, it’s smoothed off using a clean, damp trowel. This process, often called ‘trowelling up’, involves running the trowel over the surface with a bit of pressure to smooth out any imperfections. The plasterer may go over the surface several times to get it as smooth as possible.
Drying: After skimming, the wall or ceiling needs to be left to dry fully. This can take several days depending on the temperature and humidity. Once it’s fully dry, the surface should be smooth and even, ready for painting or wallpapering.
Skimming is a skill that requires practice to master. The plaster needs to be mixed to the right consistency – not too wet, not too dry – and applied evenly and smoothly. But when done correctly, it can give old, damaged walls a new lease of life, and create a perfect surface for decorating.
Float and Set
This is similar to two coat plastering, but with a different type of base coat called ‘browning’, ‘bonding’, or ‘hardwall’, depending on the surface being plastered. The base coat is applied, scratched to create a key, and then the finish coat is applied. This is often used when plastering over bricks or blocks.
Preparation: As with other plastering techniques, the first step in the Float and Set process is to prepare the surface. This involves removing any existing plaster, dust, loose materials, and ensuring the surface is clean and dry. It may also involve applying a primer or sealer, especially when working with porous surfaces like brick or block.
First Coat – Float Coat: The first coat is applied using a plastering trowel. The material used for this coat varies depending on the surface being plastered, but it’s usually one of the following: browning, bonding, or hardwall. These are all gypsum-based undercoat plasters, but they have different properties:
- Browning is used for porous surfaces like bricks and blocks.
- Bonding is used for lower suction surfaces like concrete.
- Hardwall is quicker drying and more impact-resistant, making it suitable for high traffic areas.
The plaster is mixed with water to form a thick paste, which is then applied to the wall or ceiling to a thickness of about 10-12mm. The plaster should cover the entire surface, filling in any gaps or holes.
Once the plaster starts to dry but is still soft, it’s then scratched with a tool (like a comb or scarifier) to create a ‘key’. This key allows the second coat to adhere better to the first coat.
Second Coat – Set Coat: The second coat, or set coat, is applied after the first coat has dried sufficiently. This is usually a finishing plaster, which is finer and smoother than the undercoat plaster used for the first coat. The set coat is applied to a thickness of about 2mm.
After the set coat is applied, the plasterer waits for it to start setting before smoothing it with a clean, damp trowel. This process, known as ‘trowelling up’, may be repeated several times to achieve the desired smoothness.
Drying: Finally, the plaster is left to dry completely. This can take several days, depending on the conditions. Once it’s dry, it’s ready for painting or wallpapering.
The Float and Set technique is often used when plastering over bricks or blocks, as it provides a robust, smooth surface. It does require skill and experience to execute well, especially to get a smooth finish and avoid problems like cracking or delamination. But when done correctly, it can provide a high-quality, durable finish that’s suitable for both domestic and commercial properties.
Dot and Dab (Dry Lining)
Dot and Dab, also known as Dry Lining, is a technique used to fix plasterboard to walls using a special adhesive. This technique is particularly useful for quickly covering large areas, insulating walls, or when the walls are not suitable for wet plaster. It’s a popular method in the UK for its speed and efficiency. Here’s a more detailed look at the process:
Preparation: As with all plastering techniques, proper preparation is key. The wall surface needs to be clean, dry, and free of dust and loose material. Any significant irregularities or protrusions on the wall may need to be removed or filled to ensure the plasterboard can fit flat against the wall.
Applying the Adhesive: The adhesive used in this process is typically a drywall adhesive, which is mixed with water to create a thick paste. This adhesive is applied to the wall in dabs, hence the name ‘Dot and Dab’. The dabs are usually about the size of a fist and are applied at intervals of about 30-40 cm both vertically and horizontally.
Attaching the Plasterboard: Once the adhesive has been applied, the plasterboard is pressed onto it. It’s important to ensure the board is level and that it makes good contact with all the adhesive dabs. The plasterboard is usually cut to fit the wall perfectly, with cutouts for any doors, windows, or fixtures.
Once the plasterboard is in place, it’s tapped with a straight edge (like a spirit level) to ensure it’s flush against the wall and that the adhesive is evenly spread behind it. If necessary, more dabs of adhesive can be added to fill in any gaps.
Drying: The adhesive is then left to dry, which usually takes at least 24 hours. During this time, it’s important to avoid disturbing the plasterboard, as this could weaken the bond.
Skimming: Once the adhesive is dry, the plasterboard is usually skimmed over with a thin layer of finishing plaster. This creates a smooth, even surface that’s ready for decorating. The plaster is applied with a trowel and smoothed over several times to get the perfect finish. Once the plaster is dry, it can be painted or wallpapered as desired.
Dot and Dab is a relatively straightforward technique, but it still requires skill to get a good result. It’s important to ensure the plasterboard is level and securely fixed, and that the plaster is smoothly applied. But when done correctly, it can provide a quick and effective way to cover walls and improve insulation.
Drywall Plastering (aka Taping and Jointing
Drywall plastering, also known as taping and jointing, is a method of finishing the joints between sheets of plasterboard or drywall to create a seamless, smooth surface. This technique is often used in construction or remodeling, especially in North America, as it is faster and less messy than traditional wet plastering techniques. Let’s explore this in more detail:
Frame Installation: The process begins by installing a frame made of either timber or metal studs on the wall. This frame provides the structure to which the drywall will be attached.
Drywall Installation: Drywall sheets, also known as plasterboard, are then fixed to the frame using special drywall screws. The drywall is cut to fit the wall precisely, and holes are made for any windows, doors, electrical outlets, or other features. The sheets are typically installed horizontally, and the screws are spaced evenly along the studs to securely attach the drywall to the frame.
Taping: Once the drywall is in place, the joints between the sheets are taped over using a special drywall joint tape. This tape can be either paper or a mesh made of fibreglass. The tape is applied along the length of each joint, covering the gap between the sheets of drywall.
Applying Jointing Compound: After the tape is in place, a thin layer of joint compound (also known as ‘mud’) is applied over the tape using a trowel or a special tool called a ‘mud box’. The joint compound is also used to cover the heads of the screws that were used to fix the drywall to the frame.
The joint compound needs to be applied smoothly and evenly, feathering it out at the edges to blend with the drywall. This ensures that the joints are not visible once the wall is finished.
Sanding and Finishing: After the joint compound has dried, it is then sanded smooth. This might need to be done a couple of times, applying a thin layer of joint compound and then sanding it down, to achieve a completely smooth surface.
Once the joint compound has been sanded and is smooth, the drywall is ready for decorating – it can be painted, wallpapered, or otherwise finished as desired.
Drywall plastering is a faster and less labour-intensive alternative to traditional plastering techniques, but it still requires skill and experience to achieve a good result. The joint compound needs to be applied smoothly, and the sanding process can be dusty and time-consuming. But when done correctly, drywall plastering can provide a smooth, seamless surface that’s ready for decorating.